Pneumatic pumps are used in the automotive sector, for example, for filling the seat bladders with air to change the contour of the seat's sitting and backrest areas. A pump used for the purpose named above, for example, has at least one pump chamber. By enlarging and reducing the chamber volume with the help of a drive unit, surrounding air is suctioned into the pump chamber during volume enlargement and air is driven out from the pump chamber during volume reduction. To control the corresponding air flows, the pump is equipped with an inlet valve that has a valve element for controlling the inlet opening. The inlet valve opens autonomously when the pump chamber enlarges and air flows into it from the surroundings. An outlet valve serves for controlling the outgoing airflow. It is likewise equipped with a valve element, but it controls an outlet opening which opens when air is driven out of the pump chamber.
A pump of the type described above is additionally equipped with a pressure relief valve used especially when a vehicle's seat bladders are being filled because they can leak under an excess pressure load. The pressure relief valve, in turn, has a valve element that closes a pressure relief opening and in closing direction rests on a spring element arranged in a spring space. When the pressure in the pump chamber exceeds a preset value, the excess pressure valve opens when there is a limit pressure set by the spring element. With regard to the respectively permissible maximum pressure of the pneumatic system or of a designed part thereof, the limit pressure can vary depending on the application. So far, the approach has been to use springs of various strengths in the assembly of the pump, but this entails a corresponding logistical and technical assembly effort. Additionally, there is the risk of that the wrong springs could be fit into the pump during assembly.